Apparatus and methods for manufacturing operations using non-contact position sensing

ABSTRACT

Apparatus and methods for manufacturing operations using non-contact position sensing are disclosed. In one embodiment, an apparatus includes a track assembly adapted to be attached to a workpiece, a carriage assembly moveably coupled to the track assembly and moveable relative to the workpiece, and a position sensor. The position sensor includes a sensor element adapted to detect at least one edge of an index feature on the workpiece from a distance away from the index feature. In an alternate embodiment, the position sensor may include a sensing circuit that receives an analog signal from the sensing element and provides both analog and digital output signals. In another embodiment, a controller that controls manufacturing operations may be mounted directly on the carriage assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to co-pending, commonly-ownedU.S. patent application Ser. No. 10/016,524 entitled “Flexible TrackDrilling Machine” filed Dec. 10, 2001, and to the followingconcurrently-filed, commonly-owned U.S. patent applications: “Methodsand Apparatus for Counterbalance-Assisted Manufacturing Operations”bearing attorney docket number BING-1-1002, “Apparatus and Methods forManufacturing Operations Using Opposing-Force Support Systems” bearingattorney docket number BING-1-1003, “Methods and Apparatus for TrackMembers Having a Neutral-Axis Rack” bearing attorney docket numberBING-1-1004, and “Apparatus and Methods for Servo-ControlledManufacturing Operations” bearing attorney docket number BING-1-1006.

FIELD OF THE INVENTION

[0002] The present disclosure relates to apparatus and methods formanufacturing operations using non-contact position sensing.

BACKGROUND OF THE INVENTION

[0003] The fabrication of large structures may involve the performanceof a large number of manufacturing operations on the structure, such asthe drilling of a large number of holes. Conventional structures thatrequire a large number of manufacturing operations include, for example,aircraft, missiles, ships, railcars, sheet metal buildings, and othersimilar structures. In particular, conventional aircraft fabricationprocesses typically involve the drilling of a large number of holes inwing sections of the aircraft to allow these sections to be attached toeach other and to the airframe.

[0004] A variety of devices have been developed to facilitate drillingoperations involving the drilling of a large number of holes. Forexample, U.S. Pat. No. 4,850,763 issued to Jack et al. discloses adrilling system that includes a pair of rails temporarily attached to anaircraft fuselage. A support carriage is slideably coupled to the railsand supports a drill assembly. A template attached to the aircraftfuselage provides an indication of the desired locations of the holesthat are to be formed in the aircraft fuselage. As the carriage is movedalong the rails, a locking mechanism (or trigger) interacts with thetemplate to securely position the carriage for a subsequent drillingoperation.

[0005] Although desirable results have been achieved using the prior artdrilling systems, there is room for improvement. For example, prior artassemblies typically need to be carefully oriented on the workpieceprior to performing manufacturing operations to ensure that themanufacturing operations are performed in the proper locations.Orienting the prior art assemblies on the workpiece may require physicalcontacts between the support carriage or other portions of the assemblyand one or more contact points on the workpiece. Such physical contactsmay be subject to degradation, especially through repeated usage, andmay also adversely impact the quality of some types of workpiecesurfaces. Therefore, a need exists for an improved position orientationsystem for performing manufacturing operations on a workpiece.

[0006] Furthermore, prior art manufacturing assemblies typically includea controller that is positioned remotely from the support carriage thatsupports a tool assembly over the workpiece, as disclosed, for example,in U.S. Pat. No. 6,550,129 B1 issued to Buttrick and U.S. Pat. No.6,073,326 issued to Banks et al. In such systems, control signals forcommanding movement of the support carriage and for controllingmanufacturing operations using the tool assembly are transmitted via asystem of control cables that extend between the remotely-positionedcontroller and the components of the support carriage and the toolassembly. Although desirable results have been achieved using suchmanufacturing assemblies, the extent of movement of the support carriageand the operation of the tool assembly may be limited by the lengths ofthe control cables or by the mobility of the controller within theconfines of the manufacturing environment.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to apparatus and methods formanufacturing operations using position sensing. Apparatus and methodsin accordance with the present invention may advantageously improve theaccuracy, efficiency, and throughput of manufacturing operations on aworkpiece.

[0008] In one embodiment, an apparatus for performing a manufacturingoperation on a workpiece includes a track assembly adapted to beattached to the workpiece, a carriage assembly moveably coupled to thetrack assembly and moveable relative to the workpiece, and a positionsensor. The position sensor is operatively coupled to the carriageassembly and includes a sensor element adapted to be operativelypositioned relative to the workpiece. The sensor element is furtheradapted to detect at least one edge of an index feature on the workpiecefrom a distance away from the index feature. Because the sensor elementdetects an edge of the index feature from a distance away from the indexfeature, the sensor element advantageously does not physically contactthe index feature, and may therefore provide improved reliability andmaintainability in comparison with prior art systems.

[0009] In another embodiment, an apparatus for performing amanufacturing operation on a workpiece includes a track assembly adaptedto be attached to the workpiece, a carriage assembly moveably coupled tothe track assembly and moveable relative to the workpiece, and aposition sensor operatively coupled to the carriage assembly. Theposition sensor includes a sensor element adapted to be operativelypositioned relative to the workpiece, and a sensing circuit having afirst portion coupled to the sensing element, the first portion beingadapted to receive an analog input signal and provide a conditionedanalog output signal on a first output node. The sensing circuit furtherincludes a second portion coupled to the first portion and adapted toreceive the conditioned analog output signal and to provide a digitaloutput signal on a second output node. Thus, the sensor elementadvantageously provides both analog and digital output signals to therelevant controller apparatus, thereby improving the versatility andaccuracy of the manufacturing system.

[0010] In a further embodiment, an apparatus for performing amanufacturing operation on a workpiece including a track assemblyadapted to be attached to the workpiece, a carriage assembly moveablycoupled to the track assembly and including a drive assembly operable totranslate the carriage assembly along the track assembly, and acontroller mounted on the carriage assembly and operatively coupled tothe drive assembly. The controller is adapted to transmit controlsignals to the drive assembly to control movement of the carriageassembly over the workpiece. Because the controller is mounted on thecarriage assembly, the carriage assembly may operate autonomously toperform manufacturing operations on the workpiece, and the amount ofsupport equipment may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The preferred and alternative embodiments of the presentinvention are described in detail below with reference to the followingdrawings.

[0012]FIG. 1 is a front elevational view of a manufacturing assemblyhaving a position sensor assembly in accordance with an embodiment ofthe invention;

[0013]FIG. 2 is an upper isometric view of a track assembly and acarriage assembly of the manufacturing assembly of FIG. 1;

[0014]FIG. 3 is another upper isometric view of the track assembly and aportion of the carriage assembly of FIG. 2;

[0015]FIG. 4 is a lower isometric view of the track assembly and aportion of the carriage assembly of FIG. 2;

[0016]FIG. 5 is an enlarged, partial isometric view of a sensor assemblyand control assembly of the manufacturing assembly of FIG. 1;

[0017]FIG. 6 is a side isometric view of a sensor of the sensor assemblyof FIG. 5;

[0018]FIG. 7 is a bottom isometric view of the sensor of FIG. 6;

[0019]FIG. 8 is a flowchart of a method of position determination inaccordance with an embodiment of the invention;

[0020]FIG. 9 is a schematic representation of the method of positiondetermination of FIG. 8;

[0021]FIG. 10 is a graph of a representative signal level of a sensorsweep used to detect a position of an index feature in accordance withan embodiment of the invention;

[0022]FIG. 11 is a control circuit for performing a positiondetermination in accordance with another alternate embodiment of theinvention; and

[0023]FIG. 12 is a schematic representation of a manufacturing assemblyin accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention relates to apparatus and methods formanufacturing operations using position sensing. Many specific detailsof certain embodiments of the invention are set forth in the followingdescription and in FIGS. 1-12 to provide a thorough understanding ofsuch embodiments. One skilled in the art, however, will understand thatthe present invention may have additional embodiments, or that thepresent invention may be practiced without several of the detailsdescribed in the following description.

[0025]FIG. 1 is a front elevational view of a manufacturing assembly 100having a position sensor assembly 140 in accordance with an embodimentof the invention. In this embodiment, the manufacturing assembly 100includes a track assembly 110 attachable to a workpiece 20, and acarriage assembly 120 moveably coupled to the track assembly 110. Acontroller 130 is operatively coupled to the position sensor assembly140 and to the carriage assembly 120. As described more fully below, themanufacturing assembly 100 having the position sensor assembly 140 mayadvantageously improve the accuracy and efficiency of manufacturingoperations performed on the workpiece 24.

[0026]FIGS. 2-4 are upper and lower partial isometric views of the trackassembly 110 and the carriage assembly 120 of FIG. 1 with the positionsensor assembly 140 removed. In this embodiment, the track assembly 110includes a pair of flexible rails 12, each rail 12 being equipped with aplurality of vacuum cup assemblies 14. The vacuum cup assemblies 14 arefluidly coupled to one or more vacuum lines 16 leading to a vacuumsource 18, such as a vacuum pump or the like, such that vacuum may becontrollably applied to (and removed from) the vacuum cup assemblies 14during, for example, mounting, re-positioning, and removal of the trackassembly 110 to and from the workpiece 20. The vacuum cup assemblies 14are of known construction and may be of the type disclosed, for example,in U.S. Pat. No. 6,467,385 B1 issued to Buttrick et al., or U.S. Pat.No. 6,210,084 B1 issued to Banks et al. In alternate embodiments, thevacuum cup assemblies 14 may be replaced with other types of attachmentassemblies, including magnetic attachment assemblies, bolts or otherthreaded attachment members, or any other suitable attachmentassemblies.

[0027] As further shown in FIGS. 1-4, the rails 22, 24 preferably have awidth substantially greater than their thickness such that they aresubstantially stiffer in bending about an axis that extends in thethickness direction (parallel to the z-axis in FIG. 2) than they areabout an axis that extends in the width direction (parallel to they-axis in FIG. 2). The rails 22, 24 are oriented approximately parallelto each other, although the lateral spacing between the rails 22, 24 canvary when the rails 22, 24 are mounted on a compound-contoured workpiecesurface. Preferably, the rails 22, 24 are rigidly affixed to each otherat only one end by a connecting member 28 a, which fixes the lateralspacing between the rails at that end. At other locations along therails 22, 24, the spacing between the rails 22, 24 can vary as noted.There can be another connecting member 28 b at the opposite end of therails 22, 24, but this connecting member 28 b may provide a “floating”connection that allows the spacing between the rails 22, 24 to adjust asneeded depending on the contour of the workpiece 20 surface.

[0028] The widths of the rails 22, 24 extend substantially parallel tothe surface of the workpiece 20 when the vacuum cup assemblies 14 areattached to the workpiece surface 102. Because the rails 22, 24 may bendrelatively easily about the widthwise directions and to twist abouttheir longitudinal axes, the rails 22, 24 may flex and twist as neededto substantially follow the surface of the workpiece 20 and the vacuumcup assemblies 14 maintain each rail at a substantially constantdistance from the surface of the workpiece 20. In this manner, the majorsurfaces of the rails 22, 24 may be substantially perpendicular to thesurface normal of the workpiece 20 at any point along each rail.

[0029] With continued reference to FIGS. 1-4, mounted on the rails 22,24 is the carriage assembly 120 that may translate along the rails 22,24 by virtue of rollers 32 that are mounted on an x-axis carriage 30 ofthe carriage 120 and engage the rails 22, 24. The x-axis carriage 30 ofthe carriage assembly 120 in the illustrated embodiment comprises aplate-shaped member. The rollers 32 are mounted along each of theopposite side edges of the x-axis carriage 30. More particularly, springplates 34 and 36 (best shown in FIG. 4) are attached to the x-axiscarriage 30 adjacent to a lower surface thereof at each of the oppositeside edges of the x-axis carriage 30. The spring plates 34, 36 areaffixed to the x-axis carriage 30 at locations 37 (FIG. 4) spacedinwardly from the opposite ends of the spring plates 34, 36, such thateach spring plate has two opposite end portions that are cantileveredfrom the x-axis carriage 30. The rollers 32 are mounted on thesecantilevered end portions of the spring plates 34, 36. There are twoopposing rollers 32 mounted on each cantilevered end portion of each ofthe spring plates 34, 36. Each rail 22, 24 is received between theopposing rollers 32. The rails 22, 24 preferably have V-shaped edgesengaged by the rollers 32, and the rollers 32 are V-groove rollershaving V-shaped grooves that receive the V-shaped edges of the rails 22,24. The rollers 32 thus prevent relative movement between the rollers 32and rails 22, 24 in the direction along the rotational axes of therollers 32, which axes are substantially normal to the workpiece surface102.

[0030] The spring plates 34, 36 on which the rollers 32 are mounted mayflex and twist as needed (i.e. as dictated by the contour of theworkpiece surface 102 as the carriage assembly 120 traverses the rails22, 24) to allow a limited degree of relative movement to occur betweenthe x-axis carriage 30 and the rollers 32. This is facilitated by makingthe spring plates 34, 36 relatively narrow at their middles and wider attheir ends, so that the plates 34, 36 preferentially bend and twist atapproximately the middle rather than at the ends where the rollers 32are mounted. Thus, a limited degree of relative movement can occurbetween the x-axis carriage 30 and the rails 22, 24. The net result isthat the x-axis carriage 30 enables the carriage assembly 120 totraverse the rails 22, 24 along the x-axis (i.e. the axis parallel tothe length direction of the rails 22, 24) even though the rails 22, 24may be bending and twisting in somewhat different ways relative to eachother. In effect, the rails 22, 24 conform to the contour of theworkpiece 20 and thus, the thickness direction of the rails 22, 24 isapproximately normal to the surface of the workpiece 20 at any pointalong the path defined by the rails 22, 24. Consequently, a referenceaxis of the carriage assembly 120 (in the illustrated embodiment, az-axis normal to the plane of the x-axis carriage 30) is maintainedsubstantially normal to the workpiece 20 at any position of the carriageassembly 120 along the rails 22, 24.

[0031] As best shown in FIGS. 2 and 3, a rack 38 for a rack and pinionarrangement is mounted along the surface of the rail 24 that faces thespring plate 36, and the carriage assembly 120 includes a first motor 40and associated gearbox 42 mounted on the spring plate 36. An outputshaft from the gearbox 42 has a pinion gear 44 mounted thereon, and thespring plate 36 includes a window 46 (FIG. 3) that the pinion gear 44extends through to engage the rack 38 on the rail 24. Thus, rotation ofthe pinion gear 44 by the first motor 40 drives the carriage assembly120 along the rails 22, 24. It may be appreciated that the rail 24having the rack 38 comprises a reference rail relative to which thex-axis positioning of the carriage assembly 120 may be performed. Noattempt is necessary to determine or control the x-axis positioning ofthe carriage assembly 120 relative to the other rail 22.

[0032] To improve accuracy of the x-axis position of the carriageassembly 120, the pinion gear 44 may have a constant height relative tothe rack 38 at any point along the reference rail 24. To accomplish thisheight control, the rotation axis of the pinion gear 44 may preferablylie in the same plane as that defined by the rotational axes of the tworollers 32 mounted on the end of the spring plate 36. More particularly,the axes of the rollers 32 may be substantially parallel to each otherand substantially normal to the workpiece surface 102, and the axis ofthe pinion gear 44 may be substantially parallel to the workpiecesurface 102 and may lie in the plane of the roller axes.

[0033] As further shown in FIGS. 2-4, the carriage assembly 120 furtherincludes a y-axis carriage 50 slideably mounted atop the x-axis carriage30 so that the y-axis carriage 50 can slide back and forth along ay-axis direction perpendicular to the x-axis direction. Moreparticularly, rails 52, 54 are affixed to the opposite edges of thex-axis carriage 30, and rollers 56 are mounted on the y-axis carriage 50for engaging the rails 52, 54. A rack 58 for a rack and pinionarrangement is affixed to the x-axis carriage 30 along the edge thereofadjacent to the rail 54 (see FIG. 4). A second motor 60 and associatedsecond gearbox 62 are mounted on a plate 64 that is affixed to they-axis carriage 50 adjacent to the rack 58. The plate 64 includes awindow therethrough, and the output shaft of the second gearbox 62extends through the window and drives a pinion gear 66 that engages therack 58. Thus, rotation of the pinion gear 66 by the second motor 60drives the second base member along the rails 52, 54 in the y-axisdirection.

[0034] In operation, the manufacturing assembly 100 may be mounted ontothe workpiece 20 and vacuum may be provided to the vacuum assemblies 14,thereby securing the track assembly 110 to the workpiece 20 in a desiredposition. The carriage assembly 120 may then be moved to a desiredposition along the track assembly 110. The controller 130 may transmitcontrol signals to the first drive motor 40, rotating the first drivegear 44 which engages with the rack 38 to drive the carriage assembly120 along the track assembly 110. Similarly, the controller 130 maytransmit control signals to the second drive motor 60 to adjust theposition of the y-axis carriage 50 relative to the x-axis carriage 30.

[0035] As shown in FIG. 2, mounted atop the y-axis carriage 50 is aclamp ring assembly 70. The clamp ring assembly 70 may be used tosupport and secure the position sensor assembly 140, and also to supporta tool assembly 150 as shown in phantom lines in FIG. 2. The toolassembly 150 may be extended through a window in the y-axis carriage 50(visible in FIG. 3), and through a window in the x-axis carriage 30(visible in FIG. 4) that is elongated in the y-axis direction. The axisof the tool assembly 150 may be approximately parallel to the z-axis,and thus may be substantially normal to the workpiece 20. The toolassembly 150 may be coupled to the controller 130 via a command link 152for controlling manufacturing operations on the workpiece 20.

[0036] It will be appreciated that the tool assembly 150 may be a drillspindle module or other drilling device suitable for performing drillingoperations, including, for example, those drilling devicescommercially-available from Cooper Tools, Inc. of Lexington, S.C., WestCoast Industries, Inc. of Seattle, Wash., Recoules, S.A. ofOzoir-la-Ferriere, France, or Global Industrial Technologies, Inc. ofDallas, Tex. In alternate embodiments, the tool assembly 150 may be anyof a wide variety of manufacturing tools, including, for example,riveters, mechanical and electromagnetic dent pullers, welders,wrenches, clamps, sanders, nailers, screw guns, routers, degreasers,washers, etchers, deburring tools, lasers, tape applicators, orvirtually any other desired type of manufacturing tools or measuringinstruments.

[0037]FIG. 5 is an enlarged, partial isometric view of the positionsensor assembly 140 and the controller 130 of the manufacturing assembly100 of FIG. 1. As shown in FIG. 5, the position sensor assembly 140includes a mount 142 that is coupled to the carriage assembly 120 (e.g.to the clamp ring assembly 70), and a sensor 144 that is operativelycoupled to the mount 142. A sensor link 146 is coupled between thesensor 144 and the controller 130 for transmitting and receivingsignals.

[0038]FIGS. 6 and 7 are side and bottom isometric views, respectively,of the sensor 144 of FIG. 5. As best shown in FIG. 7, the sensor 144includes a sensing element 148 for transmitting signals toward theworkpiece 20, and for receiving reflected signals from the workpiece 20,as described more fully below. It will be appreciated that the sensor144 may be any suitable digital or analog sensing element, including,for example, those sensors commercially-available from Sunx, Inc. of DesMoines, Iowa, or from Keyence, Inc. of American, N.J. In one embodiment,the sensing element 148 may be a fiber optic sensing element, and in oneparticular embodiment, the sensing element may be a coaxial fiber opticretro-reflective sensing element. In other alternate embodiments, forexample, sensor element 148 may include cameras (e.g. DVT camera visionsystems), magnetic proximity sensors, or any other suitable sensorelement. It will be appreciated that the signals transmitted from thesensor 144 to the workpiece 20, and reflected back from the workpiece 20to the sensor 144, may be visible light, infrared or ultra-violetsignals, acoustic signals, or any other desired type of signal.

[0039] With reference to FIGS. 1 and 5, the track assembly 110 may besecured to the workpiece 20, and the carriage assembly 120 may be usedto support the position sensor assembly 140 such that the sensingelement 148 is pointed toward the workpiece 20. The position sensorassembly 140 may then be employed to locate the coordinates of one ormore indexing features (or reference points) located on the workpiece20. As described more fully below, the position sensor assembly 140provides a capability for the manufacturing assembly 100 to determine apositional orientation of the manufacturing assembly 100 based on one ormore known indexing features (e.g. a hole, a fastener, a bushing, orother feature) without physical contact between the sensor assembly 140and the workpiece 20.

[0040] In one aspect, the sensing element 148 includes a bright LEDcoaxial fiber optic cable that uses a lens system to focus incident orilluminating light onto the workpiece 20. In brief, the incident lightmay be transmitted through the center fiber of the coaxial fiber opticcable, through a lens, and may be reflected by the surface of theworkpiece 20. The reflected light may then be collected through the lensand returned to a sensor amplifier through the outer portion of thecoaxial fiber optic cable. The sensor amplified may then convert theintensity of the light into an analog electrical signal. The output fromthe sensor amplifier may be calibrated to a focal point of the lens byreading the reflected light from a standard white reflective surface. Asthe scan path encounters various features on the surface, the reflectedlight may be analyzed and when the collected data match a defined set ofparameters, a known index feature (e.g. fastener, hole, etc.) can berecognized. The signal may be read and correlated to a position on thesurface by using feedback from a positioning system. This locationinformation may then be used to position other equipment on the surfaceof the workpiece 20, making it possible to control a system of tools orprocesses, as described more fully below.

[0041]FIG. 8 is a flowchart showing a method 200 of positiondetermination using the sensor assembly 140 in accordance with anembodiment of the invention. FIG. 9 is a schematic representation of themethod 200 of position determination of FIG. 8. The steps of the method200 may be implemented using known programmable or semi-programmablecomponents and software routines. As shown in FIGS. 8 and 9, the method200 may begin at an initial step 202 in which the position sensorassembly 140 is initially positioned proximate to an indexing feature 21that is to be detected, such as by an operator manually positioning thecarriage assembly 120 at a suitable location on the track assembly 110,and the position sensor assembly 140 begins transmitting one or moredetection signals 201 onto the workpiece 20 and receiving correspondingreflected signals 203 back from the workpiece 20. Next, in step 204, thesensor 144 is either incrementally or continuously advanced along afirst path 205 in a first direction (shown as the y-direction in FIG.9).

[0042] With continued reference to FIGS. 8 and 9, as the sensor 144 isadvanced along the first path 205, the method 200 continues to transmitdetection signals 201 and monitor the received reflected signals 203 todetermine whether a first edge 207 of the index feature 21 has beendetected (step 206). If the sensor 144 is a digital sensor, the sensor144 may indicate that the edge has been reached by providing a sensoroutput that transitions from a first well-defined state indicating thatthe sensor 144 is receiving reflected signals 203 that are reflectingfrom the workpiece 20, to a second well-defined state indicated that thesensor 144 is receiving reflected signals 203 that are reflecting fromthe index feature 21. Alternately, if the sensor 144 is an analogsensor, the sensor output may be proportional to the reflected signals203 from the workpiece 20 and from the index feature 21, therebyproviding an indication of when the sensor 144 is over each component,respectively.

[0043] Eventually, based on the reflected signals 203, the first edge207 (FIG. 9) of the index feature 21 may be detected (step 206). Next,in step 208, the position of the sensor 144 may be readjusted and alocalized, slow speed (or small increment) rescan may be performed todetermine the coordinates of the first edge 207, and the coordinates ofthe first edge 207 are stored. In step 210, the method 200 determineswhether the edge that has just been detected is a second edge 209 (seeFIG. 9) of the index feature 21, and if not, the method 200 repeatssteps 204 through 208 to determine and store the coordinates of thesecond edge 209.

[0044] Next, in step 212, the method 200 uses the coordinates of thefirst and second edges 207, 209 to calculate a first center 211 alongthe first path 205, and repositions the sensor 144 at a location spacedapart from the index feature 21 with a value along the first direction(e.g. the y coordinate) that corresponds to the value of the firstcenter 211. The sensor 144 is then advanced along a second path 213(shown as the x direction in FIG. 9) in step 214, and the output fromthe sensor 144 is monitored to determine whether a first edge 215 of theindex feature 21 along the second path 213 has been detected (step 216).After the first edge 215 along the second path 213 has been detected, asdescribed above, the position of the sensor 144 may be readjusted and alocalized, slow speed (or small increment) rescan may be performed alongthe second path 213 to determine the coordinates of the first edge 215,and the coordinates of the first edge 215 along the second path 213 arestored (step 218). After storing the coordinates, the method 200 nextdetermines whether the edge that has just been detected is a second edge217 of the index feature 21 along the second path 213 (see FIG. 9) instep 220, and if not, the method 200 repeats steps 214 through 218 todetermine and store the coordinates of the second edge 217 along thesecond path 213. In step 222, the method 200 uses the coordinates of thefirst and second edges 215, 217 along the second path 213 to calculate asecond center 219 (FIG. 9).

[0045] With reference to FIG. 8, steps 204 through 212 may generally bereferred to as a first sweep 224 of the sensor 144, and steps 214through 222 may be referred to as a second sweep 226 of the sensor 144.After determining the coordinates of the first and second centers 211,219 using the first and second sweeps 224, 226, the method 200 maysimply assume that the coordinates of an index center of the indexfeature 21 are the same as the coordinates of the second center 219. Ifthis approach is deemed satisfactory in step 228, then the method 200proceeds with outputting the coordinates of the center of the indexfeature 21 in step 230. If additional accuracy or confirmation isdesired, however, the method 200 may include one or more additionalsweeps 232 of the sensor 144.

[0046] As shown in FIG. 8, in an additional sweep 232 is desired, thesensor 144 is repositioned in step 234 to a location spaced apart fromthe index feature 21 but having the same value along the seconddirection (x coordinate in FIG. 9) as the second center 219. Next, thesensor 144 is advanced along a third path 213 (shown as the y directionin FIG. 9) in step 236, and the output from the sensor 144 is monitoredto determine whether a first edge 223 of the index feature 21 along thethird path 221 has been detected (step 236). After the first edge 223along the third path 221 has been detected, the position of the sensor144 may be readjusted and a localized, slow speed (or small increment)rescan may be performed along the third path 221 to determine thecoordinates of the first edge 223, and the coordinates of the first edge223 along the third path 221 are stored (step 240). After storing thecoordinates, the method 200 next determines whether the edge that hasjust been detected is a second edge 225 of the index feature 21 alongthe third path 221 (step 242). If not, the method 200 repeats steps 236through 240 to determine and store the coordinates of the second edge225 along the third path 221. In step 246, the method 200 uses thecoordinates of the first and second edges 223, 225 along the third path221 to compute a third (or additional) center 227.

[0047] After the additional sweep 232 is conducted, the method 200 mayagain determine whether the desired degree of accuracy has been reachedin step 228. If not, additional sweeps similar to the third sweep 232may be conducted along, for example, different paths. If additionalsweeps are not desired, then the method 200 proceeds to step 230, andthe coordinates of the index center are output. The results of the thirdsweep 232 (or more sweeps) may provide an improved indication of theindex center of the index feature 21. For example, the index center maybe determined as the average of the coordinates of the second and thirdcenters 219, 227. After the index center of the index feature 21 isoutput (step 230), the method 200 may continue in step 248 to the nextphase of manufacturing operations.

[0048] It may be appreciated that the particular locations anddirections of the first, second, and third paths 205, 213, 221 of themethod 200 may be varied from the particular embodiment shown in FIG. 9,and that the present invention is not limited to the particular detailsdescribed above and shown in the accompanying figure. For example, thefirst direction of the first path may be along the x axis, and thesecond direction of the second path may be along the y axis, oralternately, the first and second paths may be along any desireddirections across the index feature 21. Preferably, however, the firstand second paths are orthogonally oriented. It may also be appreciatedthat the method 200 may be better suited for locating an index center ofan index feature having a round (or approximately round) shape, althoughother shapes of index features may be employed and detected using theapparatus and methods in accordance with the present invention.

[0049]FIG. 10 is a graph 300 of a representative sensor output signallevel 302 of a sensor sweep 304 used to detect a position of an indexfeature 21 in accordance with an embodiment of the invention. In thisembodiment, the index feature 21 is a fastener head that is raised abovethe surface of the surrounding workpiece 20. The signal level 302 ofFIG. 10 may be provided by an analog type of sensor 144. As shown inFIG. 10, during a first portion A of a sensor sweep 304, the signallevel 302 is characterized by a generally constant level as reflectedsignals are receive by the sensor 144 from the surface of the workpiece20. In a second portion B, the signal level 302 is characterized by adescending level of reflected signals received by the sensor 144 as thedetection signals begin to impinge on and reflect from a leading edge306 of the fastener head 21.

[0050] As further shown in FIG. 10, as the sensor sweep 304 continues,the signal level 302 reaches a first minimum reflection value at alocation C, and then enters a portion D that is characterized by anascending signal level as an increasing level of reflected signals arereceived by the sensor 144. Next, the signal level generally levels offduring a next portion E of the sensor sweep 304 as the sensor 144 beginsreceiving a relatively constant level of reflected signals from the topof the fastener head 21. Continuing the sensor sweep 304 across the topof the fastener head 21 to a trailing edge 308 of the fastener head 21,the signal level 302 eventually is characterized by a relativelysubstantial descent to a second minimum reflection level at a locationF, and then rises again to an ambient reflection level characteristic ofreflections from the surface of the workpiece 20. In one embodiment, themethod 200 described above with reference to FIGS. 8 and 9 performs theabove-referenced edge determinations (steps 206, 208, 216, 218, 238, and240) by assigning the coordinates of the sensor 144 corresponding to thelocations of the first and second minimum reflection levels (locations Cand F) as being the coordinate positions of the first and second edgesfor each of the paths 205, 213, 221.

[0051] More specifically, the leading and trailing edges 306, 308 may becomputed from the signal level 302 by first computing an ambientreflectivity level (portion A), such as by computing a running averageof the sensor level 302. During the sensor sweep 304, as the sensorlevel 302 drops below a predetermined threshold, such as a predeterminedpercentage of the ambient reflectivity level, an edge detectionprocedure may be invoked. The edge detection procedure may store theminimum sensor value (location C) corresponding to the leading edge 306and the position coordinates thereof, and may also store the sameinformation from the minimum sensor value corresponding to the trailingedge 308 (location F). A center may then be mathematically computed fromthe positions of the two minimum sensor values (locations C and F).

[0052] It will be appreciated that the characteristics of the sensorlevel may vary, and that various index features may provide sensorlevels having different shapes, trends, and characteristics than thatshown in the graph 300 of FIG. 10. Similarly, it may be desirable tomonitor different aspects of the sensor level other than the locationsof the minimum sensor values, such as, for example, the derivative (orslope) of the sensor levels. In one alternate embodiment, for example,the index feature may be a bushing having a concave rolled edge. Forsuch a bushing, the edges of the bushing may be more readily determinedby monitoring a derivative of the sensor level (e.g. with respect to thedistance traveled by the sensor 144) during a sensor sweep over thebushing. In that case, the peaks or maxima of the derivative values maybe representative of the rate of change of the profile of the surfacesover which the sensor 144 is swept, effectively shifting the pattern intime by a constant of differentiation.

[0053] In operation, the position sensor assembly 140 may be employed todetermine the locations of one or more index features 21 on theworkpiece 20, thereby precisely defining the position of themanufacturing assembly 100 on the workpiece 20. This information maythen be stored in a memory device of the controller 130. After theposition sensor assembly 140 has been employed for this purpose, theposition sensor assembly 140 may be removed from the carriage assembly120, and the tool assembly 150 may be installed on the carriage assembly120. Using command and control information stored in its memory device,the controller 130 may then autonomously control the carriage assembly120 and the tool assembly 150 to perform the desired manufacturingoperations at the desired locations on the workpiece 20. Different toolassemblies may be interchanged to and from the carriage assembly 120 toperform different manufacturing operations as desired.

[0054] Manufacturing assemblies having the position sensor assembly inaccordance with the teachings of the present invention mayadvantageously improve the quality and efficiency of manufacturingoperations on a workpiece. The position sensor assembly may provide arelatively fast, automated method of precisely locating themanufacturing assembly on the workpiece using an indexing feature thatmay already be part of the workpiece or the structure. The need forphysical contact index points, the accuracy of which may becomedegraded, is thereby reduced or eliminated. The need to preciselyposition the track assembly on the workpiece at the start ofmanufacturing operations is also reduced or eliminated. The positionsensor may accurately determine the location of the manufacturingassembly on the workpiece, and the data corresponding to the desiredlocations of the manufacturing operations (e.g. the hole pattern for aplurality of drilling operations) which are stored in memory may simplybe rotated or transformed in machine space into proper alignment andorientation with the actual location of the track assembly on theworkpiece using standard transformation matrix algorithms. In this way,the accuracy, consistency, and efficiency of the manufacturingoperations on the workpiece may be improved, and the costs associatedwith performing, inspecting, and reworking the workpiece may be reduced.

[0055] The manufacturing assembly 100 having the position sensorassembly 140 further provides the capability to detect an index featureon the workpiece 20 without the need for physical contact betweencontact sensors, feeler gauges, or other physical contact devices on thecarriage assembly 120 and corresponding contact features on theworkpiece 20. The sensor element may detect the index feature from adistance away from the index feature, thereby eliminating any need forphysical contact between the sensor element and the index feature.Because there is no physical contact, the position sensor assembly mayprovide improved performance over alternate sensor systems that requirephysical contact and that may be bent, damaged, or otherwise degradedduring transport, storage, or during the performance of manufacturingoperations. In this way, the position sensor assembly may improve theaccuracy of the manufacturing processes, and may reduce the laborassociated with the process of orienting the manufacturing assembly onthe workpiece. Also, the position sensor assembly may advantageouslyreduce or eliminate the possibility of damage to the surface of theworkpiece that may otherwise be caused by physical contact with thesurface, reducing the need for repairs and reworking of the workpiece.Thus, the overall efficiency and throughput of the manufacturingoperation may be improved.

[0056] It may be appreciated that a variety of alternate embodiments ofapparatus and methods may be conceived in accordance with the presentinvention, and that the invention is not limited to the particularapparatus and methods described above and shown in the accompanyingfigures. For example, it may be noted that the carriage assembly 120 andthe track assembly 110 may assume a wide variety of alternateembodiments, including, for example, the rail and carriage assembliestaught by U.S. Pat. No. 4,850,763 issued to Jack et al, and any of thecarriage assemblies and track assemblies disclosed in co-pending,commonly owned U.S. patent application Ser. No. 10/016,524, whichapplication is incorporated herein by reference.

[0057] In another aspect, a control circuit 400 may be employed thatreceives and enhances an output signal of an analog sensor of theposition sensor assembly 140. For example, FIG. 11 is a sensing circuit400 for performing a position determination in accordance with anotheralternate embodiment of the invention. In this embodiment, the sensingcircuit 400 includes a comparator stage whereby an output signal 404 ofan analog sensor 406 is made to function as a digital proximity sensorsimultaneously with its use as an analog sensor. As shown in FIG. 11,the output signal 404 is fed into a first circuit portion 408 configuredto provide a gain and level shift stage. The first circuit portion 408may provide an optimal response for different types of workpiecesurfaces. A conditioned analog signal 410 output by the first circuitportion 408 is provided to the controller 130 on an analog output node412. Similarly, the conditioned analog signal 410 output by the firstcircuit portion 408 is provided as an input to a second circuit portion414. The second circuit portion 414 is configured as a thresholdcomparator stage which trips above or below a given signal voltage,providing an appropriate digital signal 416 on a digital output node418. The gain, offset, and threshold values of the sensing circuit 400may be predetermined constants, or may be programmable by the controller130 according to varying operating conditions.

[0058] Manufacturing assemblies that includes the sensing circuit 400may provide improved position accuracy over alternate systems. Becausethe sensing circuit 400 may receive an analog signal from the sensingelement and provides both a conditioned analog output and a digitaloutput, the sensing circuit may provide a capability of cross-checkingthe results of the position detection of an index feature by enablingthe controller to compare and utilize both analog and digital outputsignals. The sensing circuit 400 may also provide improved versatilityby enabling the position sensor assembly to be utilized with both analogor digital controllers or other desired electronic components.

[0059] It may be appreciated that the various operations of themanufacturing assembly 100 may be controlled by the controller 130,including the positioning of the carriage assembly 120 on the trackassembly 110, the operations of the position sensor assembly 140, andthe positioning and engagement of the tool assembly 150 with respect tothe workpiece 20. These operations may be accomplished in an automatedor semi-automated manner using the controller 134 equipped withcomputerized numerically-controlled (CNC) methods and algorithms.Alternately, the positioning may be performed manually orpartially-manually by an operator, such as, for example, by having theoperator provide manual control inputs to the controller 134, or bytemporarily disabling or neutralizing the above-referenced motors andactuators of the carriage and clamp-up assemblies 120, 160 to permitmanual movement.

[0060] Typically, to provide a desired degree of positional accuracy forperforming manufacturing operations, the index centers of two indexfeatures 21 may be determined using the methods and apparatus describedabove. After the one or more index centers of the index features 21 havebeen determined, control algorithms of the manufacturing assembly 100may be used to transform a data pattern stored in a memory of a controlsystem (e.g. in the controller 130) into machine space for controllingthe manufacturing operations performed by the manufacturing assembly 100on the workpiece 20. These transformations may be performed usingstandard, well-known mathematical algorithms commonly employed inpresently-existing CNC machining processes.

[0061] Referring again to FIGS. 1 and 5, in yet another aspect, thecontroller 130 may include an entire CNC control system. For example, inone particular embodiment, the controller 130 includes an 8-axisservo-controller, and a plurality of servo-amplifiers, servo-motors, andair solenoids. Because the controller 130 is attached directly to thecarriage assembly 120 (e.g. to the y-axis carriage 50), the controller130 travels with the carriage assembly 120 during the performancemanufacturing operations. Thus, the links or cables between thecontroller 130 and the other components of the manufacturing assembly100 for transmitting control signals to (and receiving feedback signalsfrom) the drive motors 40, 60 of the carriage assembly 120, the positionsensor assembly 140, the tool assembly 150, and any other components ofthe manufacturing assembly, are greatly reduced or eliminated. Acontroller umbilical 132 (FIG. 1) may provide control air, electricalpower, and communication cables from a supply unit 134 to the controller130. Alternately, the controller umbilical 132 may also providehigh-volume fluid (e.g. air or hydraulics) for powering the toolassembly 150.

[0062] The manufacturing assembly 100 having the controller 130 mountedto the carriage assembly 120 may further improve the efficiency andthroughput of the manufacturing operations. Because the controller 130is mounted on the carriage assembly 120, the amount of cables extendingbetween the controller 130 and the portions of the carriage assembly(e.g. the drive assembly, the position sensor assembly, etc.) and thetool assembly 150 may be reduced compared with prior art manufacturingassemblies. Thus, the manufacturing assembly may provide improvedmobility of the carriage assembly over the track assembly because themovement of the carriage assembly is not limited by the lengths of thecontrol cables extending between the carriage assembly to aremotely-located controller, or by the mobility of a remotely-locatedcontroller within the confines of the manufacturing environment. Thecombination of the carriage assembly 120 and the controller 130 may evenallow for a single operator to move these components between variouslocations to conduct manufacturing operations at different locations oron different workpieces, thereby further improving the efficiency andthroughput of the manufacturing process.

[0063]FIG. 12 is a schematic representation of a manufacturing assembly500 in accordance with yet another embodiment of the invention. In thisembodiment, the manufacturing assembly 500 includes a sensor unit 502and a pair of tool units 504 operating on a track assembly 110 (notvisible) that is coupled to a contoured workpiece 520. The sensor andtool units 502, 504 each include a carriage assembly as described above.The sensor unit 502 also includes a position sensor assembly 140, whilethe tool units 504 include a tool assembly 150. The sensor and toolunits 502, 504 are operatively coupled to a master controller 506, suchas by wireless or hardwired communication links 508. The sensor and toolunits 502, 504 may also include a controller 130, as described above.

[0064] In operation, each of the sensor and tool units 502, 504 mayoperate autonomously under the control of their respective controllers130, or semi-autonomously under the control of both the controller 130and the master controller 506, or may be fully controlled by the mastercontroller 506. In one embodiment, the sensor unit 502 may perform thefunction of locating various indexing features distributed over theworkpiece 520 in the manner described above, which information may betransmitted to the master controller 506. The master controller 506 maythen provide command and control signals to one or more tool units 504to precisely position the tool units 504 and to perform the desiredmanufacturing operations on the workpiece 520. Alternately, thelocations of the indexing features may be transmitted from the sensorunit 502 directly to one or more of the tool units 504, and the toolunits 504 may operate autonomously to perform the desired manufacturingoperations at the appropriate locations on the workpiece 520. Afterlocating the indexing features on a first portion of the workpiece 520,the sensor unit 502 may move automatically to a next portion, or may becommanded to proceed to the next portion of the workpiece 520 by themaster controller 506 to make room for the tool units 504 or to locateadditional index features.

[0065] The manufacturing assembly 500 may further improve the efficiencyand throughput of manufacturing operations. As noted above, because thecontroller 130 of each unit 502, 504 is mounted to the carriage assembly120, the number of cables and wires associated with each unit 502, 504may be reduced, thereby improving the mobility of each unit over theworkpiece 520. Because the need for cables extending between each of theunits 502, 504 and a remotely-located controller may be reduced, thenumber of different units 502, 504 that may be located and operated inrelatively close proximity on a single track assembly may be increased.Thus, the efficiency and throughput of manufacturing operations may beimproved.

[0066] While specific embodiments of the invention have been illustratedand described herein, as noted above, many changes can be made withoutdeparting from the spirit and scope of the invention. Accordingly, thescope of the invention should not be limited by the disclosure of thespecific embodiments set forth above. Instead, the invention should bedetermined entirely by reference to the claims that follow.

What is claimed is:
 1. An apparatus for performing a manufacturingoperation on a workpiece, the apparatus comprising: a track assemblyadapted to be attached to the workpiece; a carriage assembly moveablycoupled to the track assembly and moveable relative to the workpiece;and a position sensor operatively coupled to the carriage assembly andincluding a sensor element adapted to be operatively positioned relativeto the workpiece, the sensor element being adapted to detect at leastone edge of an index feature on the workpiece from a distance away fromthe index feature.
 2. The apparatus of claim 1, wherein the sensorelement includes a fiber optic sensing element.
 3. The apparatus ofclaim 1, wherein the sensor element is adapted to detect the at leastone edge of the index feature as the sensor element is being moved overthe workpiece by the carriage assembly.
 4. The apparatus of claim 1,further comprising a controller operatively coupled to the positionsensor, the controller being adapted to receive a first edge detectionsignal from the position sensor indicating that a first edge of theindex feature has been detected along a first path of movement of theposition sensor, and to receive a second edge detection signal from theposition sensor indicating that a second edge of the index feature hasbeen detected along the first path, and to compute a midpoint locationbased on the first and second edge detection signals.
 5. The apparatusof claim 4, wherein the controller is further adapted to receive thirdand fourth edge detection signals from the position sensor indicatingthat third and fourth edges of the index feature have been detectedalong a second path of movement of the position sensor, respectively,and is also adapted to compute an estimated center of the index featurebased on the first, second, third, and fourth edge detection signals. 6.The apparatus of claim 1, further comprising a controller mounted on thecarriage assembly and operatively coupled to the position sensor.
 7. Theapparatus of claim 6, wherein the carriage assembly includes a driveassembly operable to translate the carriage assembly along the trackassembly, the drive assembly being operatively coupled to thecontroller.
 8. The apparatus of claim 7, wherein the drive assembly isfurther operable to translate the position sensor in a direction that istransverse to the track assembly.
 9. The apparatus of claim 1, whereinthe position sensor includes a sensing circuit having a first portioncoupled to the sensing element, the first portion being adapted toreceive an analog input signal and provide a conditioned analog outputsignal on a first output node, the sensing circuit further including asecond portion coupled to the first portion and adapted to receive theconditioned analog output signal and to provide a digital output signalon a second output node.
 10. The apparatus of claim 9, wherein the firstportion of the sensing circuit is adapted to provide a gain and levelshift of the analog input signal.
 11. The apparatus of claim 9, whereinthe second portion of the sensing circuit includes a thresholdcomparator circuit adapted to provide a first digital output signal whenthe conditioned analog output signal is below a threshold level, and toprovide a second digital output signal when the conditioned analogoutput signal is above the threshold level.
 12. The apparatus of claim9, wherein the first portion of the sensing circuit is adapted toprovide a gain and level shift of the analog input signal, and whereinthe second portion of the sensing circuit includes a thresholdcomparator circuit adapted to provide a first digital output signal whenthe conditioned analog output signal is below a threshold level, and toprovide a second digital output signal when the conditioned analogoutput signal is above the threshold level, at least one of the gain andthreshold level being programmable.
 13. The apparatus of claim 1,further comprising a tool assembly coupled to the carriage assembly andengageable with the workpiece to perform the manufacturing operation onthe workpiece.
 14. An apparatus for performing a manufacturing operationon a workpiece, the apparatus comprising: a track assembly adapted to beattached to the workpiece; a carriage assembly moveably coupled to thetrack assembly and moveable relative to the workpiece; and a positionsensor operatively coupled to the carriage assembly and including asensor element adapted to be operatively positioned relative to theworkpiece, and a sensing circuit having a first portion coupled to thesensing element, the first portion being adapted to receive an analoginput signal and provide a conditioned analog output signal on a firstoutput node, the sensing circuit further including a second portioncoupled to the first portion and adapted to receive the conditionedanalog output signal and to provide a digital output signal on a secondoutput node.
 15. The apparatus of claim 14, wherein the first portion ofthe sensing circuit is adapted to provide a gain and level shift of theanalog input signal.
 16. The apparatus of claim 14, wherein the secondportion of the sensing circuit includes a threshold comparator circuitadapted to provide a first digital output signal when the conditionedanalog output signal is below a threshold level, and to provide a seconddigital output signal when the conditioned analog output signal is abovethe threshold level.
 17. The apparatus of claim 14, wherein the firstportion of the sensing circuit is adapted to provide a gain and levelshift of the analog input signal, and wherein the second portion of thesensing circuit includes a threshold comparator circuit adapted toprovide a first digital output signal when the conditioned analog outputsignal is below a threshold level, and to provide a second digitaloutput signal when the conditioned analog output signal is above thethreshold level, at least one of the gain and threshold level beingprogrammable.
 18. The apparatus of claim 14, wherein the sensor elementis adapted to detect at least one edge of an index feature on theworkpiece from a distance away from the index feature.
 19. The apparatusof claim 14, wherein the sensor element includes a fiber optic sensingelement.
 20. The apparatus of claim 14, wherein the sensor element isadapted to detect the at least one edge of the index feature as thesensor element is being moved over the workpiece by the carriageassembly.
 21. The apparatus of claim 14, further comprising a controlleroperatively coupled to the position sensor, the controller being adaptedto receive a first edge detection signal from the position sensorindicating that a first edge of the index feature has been detectedalong a first path of movement of the position sensor, and to receive asecond edge detection signal from the position sensor indicating that asecond edge of the index feature has been detected along the first path,and to compute a midpoint location based on the first and second edgedetection signals.
 22. The apparatus of claim 21, wherein the controlleris further adapted to receive third and fourth edge detection signalsfrom the position sensor indicating that third and fourth edges of theindex feature have been detected along a second path of movement of theposition sensor, respectively, and is also adapted to compute anestimated center of the index feature based on the first, second, third,and fourth edge detection signals.
 23. The apparatus of claim 14,further comprising a controller mounted on the carriage assembly andoperatively coupled to the position sensor.
 24. The apparatus of claim23, wherein the carriage assembly includes a drive assembly operable totranslate the carriage assembly along the track assembly, the driveassembly being operatively coupled to the controller.
 25. The apparatusof claim 24, wherein the drive assembly is further operable to translatethe position sensor in a direction that is transverse to the trackassembly.
 26. The apparatus of claim 14, further comprising a toolassembly coupled to the carriage assembly and operatively coupled to thecontroller, the tool assembly being engageable with the workpiece toperform the manufacturing operation on the workpiece.
 27. An apparatusfor performing a manufacturing operation on a workpiece, the apparatuscomprising: a track assembly adapted to be attached to the workpiece; acarriage assembly moveably coupled to the track assembly and including adrive assembly operable to translate the carriage assembly along thetrack assembly; and a controller mounted on the carriage assembly andoperatively coupled to the drive assembly, the controller being adaptedto transmit control signals to the drive assembly to control movement ofthe carriage assembly over the workpiece.
 28. The apparatus of claim 27,wherein the controller includes a programmable CNC system operable toautomatically transmit control signals to the drive assembly toautomatically control movement of the carriage assembly over theworkpiece.
 29. The apparatus of claim 27, further comprising a positionsensor coupled to the carriage assembly and operatively coupled to thecontroller, the position sensor including a sensor element adapted to beoperatively positioned relative to the workpiece, and a sensing circuithaving a first portion coupled to the sensing element, the first portionbeing adapted to receive an analog input signal and provide aconditioned analog output signal on a first output node, the sensingcircuit further including a second portion coupled to the first portionand adapted to receive the conditioned analog output signal and toprovide a digital output signal on a second output node.
 30. Theapparatus of claim 29, wherein the first portion of the sensing circuitis adapted to provide a gain and level shift of the analog input signal.31. The apparatus of claim 29, wherein the second portion of the sensingcircuit includes a threshold comparator circuit adapted to provide afirst digital output signal when the conditioned analog output signal isbelow a threshold level, and to provide a second digital output signalwhen the conditioned analog output signal is above the threshold level.32. The apparatus of claim 29, wherein the first portion of the sensingcircuit is adapted to provide a gain and level shift of the analog inputsignal, and wherein the second portion of the sensing circuit includes athreshold comparator circuit adapted to provide a first digital outputsignal when the conditioned analog output signal is below a thresholdlevel, and to provide a second digital output signal when theconditioned analog output signal is above the threshold level, at leastone of the gain and threshold level being programmable.
 33. Theapparatus of claim 27, further comprising a position sensor coupled tothe carriage assembly and operatively coupled to the controller, theposition sensor including a sensor element adapted to detect at leastone edge of an index feature on the workpiece from a distance away fromthe index feature.
 34. The apparatus of claim 33, wherein the controlleris adapted to receive a first edge detection signal from the positionsensor indicating that a first edge of the index feature has beendetected along a first path of movement of the position sensor, and toreceive a second edge detection signal from the position sensorindicating that a second edge of the index feature has been detectedalong the first path, and to compute a midpoint location based on thefirst and second edge detection signals.
 35. The apparatus of claim 34,wherein the controller is further adapted to receive third and fourthedge detection signals from the position sensor indicating that thirdand fourth edges of the index feature have been detected along a secondpath of movement of the position sensor, respectively, and is alsoadapted to compute an estimated center of the index feature based on thefirst, second, third, and fourth edge detection signals.
 36. Theapparatus of claim 27, further comprising a tool assembly coupled to thecarriage assembly and operatively coupled to the controller, the toolassembly being engageable with the workpiece to perform themanufacturing operation on the workpiece.
 37. The apparatus of claim 36wherein the carriage assembly is a first carriage assembly and thecontroller is a first controller, the apparatus further comprising: asecond carriage assembly moveably coupled to the track assembly andincluding a second drive assembly operable to translate the secondcarriage assembly along the track assembly; a second controller mountedon the second carriage assembly and operatively coupled to the seconddrive assembly, the second controller being adapted to transmit controlsignals to the second drive assembly to control movement of the secondcarriage assembly over the workpiece; and a position sensor coupled tothe carriage assembly and operatively coupled to the second controller,the position sensor including a sensor element adapted to detect atleast one edge of an index feature on the workpiece from a distance awayfrom the index feature.
 38. The apparatus of claim 37, furthercomprising a master controller operatively coupled to the first andsecond controllers and adapted to transmit control signals to the firstand second controllers, and adapted to receive feedback signals from thefirst and second controllers.
 39. A method of performing a manufacturingoperation on a workpiece, the method comprising: supporting amanufacturing assembly proximate a surface of the workpiece, themanufacturing assembly including a sensing element that is operativelypositioned relative to and spaced apart from the workpiece, the sensingelement being moveable relative to the surface of the workpiece; movingthe sensing element along a first path on the workpiece; and detectingat least one edge of an index feature on the workpiece from a distanceaway from the index feature.
 40. The method of claim 39, whereindetecting at least one edge of an index feature on the workpiece from adistance away from the index feature includes detecting a reflectedelectromagnetic signal reflected from the index feature.
 41. The methodof claim 39, wherein detecting at least one edge of an index feature onthe workpiece from a distance away from the index feature occurssimultaneously with moving the sensing element along a first path thatcrosses an index feature on the workpiece.
 42. The method of claim 39,wherein detecting at least one edge of an index feature includesdetecting first and second edges of the index feature along the firstpath, the method further comprising computing a midpoint location basedon the first and second edges.
 43. The method of claim 42, furthercomprising detecting third and fourth edges of the index feature along asecond path of movement of the position sensor, and computing anestimated center of the index feature based on the first, second, third,and fourth edges.
 44. The method of claim 39 wherein supporting amanufacturing assembly proximate a surface of the workpiece includessupporting a manufacturing assembly having a controller operativelycoupled to the sensing element, and wherein moving the sensing elementalong a first path includes transmitting at least one control signalfrom the controller.
 45. The method of claim 39 wherein supporting amanufacturing assembly proximate a surface of the workpiece includessupporting a manufacturing assembly having a drive assembly operable tomove the sensing element relative to the workpiece, and further having acontroller mounted on the carriage assembly and operatively coupled tothe drive assembly.
 46. The method of claim 39, further comprisingproviding at least one output signal indicating a location of the atleast one edge of the index feature.
 47. The method of claim 46, whereinproviding at least one output signal includes providing an analog outputsignal.
 48. The method of claim 47, wherein providing an analog outputsignal includes applying a gain and level shift of an analog inputsignal to provide a conditioned analog output signal.
 49. The method ofclaim 48, wherein providing at least one output signal further includesproviding a digital output signal.
 50. The method of claim 49, whereinproviding a digital signal includes providing a first digital outputsignal when the conditioned analog output signal is below a thresholdlevel, and providing a second digital output signal when the conditionedanalog output signal is above the threshold level.
 51. The method ofclaim 39, wherein supporting a manufacturing assembly proximate asurface of the workpiece includes supporting a manufacturing assemblyhaving a tool assembly engageable with the workpiece, the method furthercomprising operatively engaging the tool assembly with the workpiece.52. A method of performing a manufacturing operation on a workpiece, themethod comprising: supporting a manufacturing assembly proximate asurface of the workpiece, the manufacturing assembly including a sensingelement that is operatively positioned relative to and spaced apart fromthe workpiece, the sensing element being moveable relative to thesurface of the workpiece; moving the sensing element along a first pathon the workpiece; detecting at least one edge of an index feature on theworkpiece; providing a conditioned analog output signal indicating alocation of the at least one edge of the index feature; and providing adigital output signal indicating the location of the at least one edgeof the index feature.
 53. The method of claim 52, wherein providing ananalog output signal includes applying a gain and level shift of ananalog input signal to provide the conditioned analog output signal. 54.The method of claim 52, wherein providing a digital signal includesproviding a first digital output signal when the conditioned analogoutput signal is below a threshold level, and providing a second digitaloutput signal when the conditioned analog output signal is above thethreshold level.
 55. The method of claim 52, wherein providing detectingat least one edge of an index feature on the workpiece includesdetecting at least one edge of an index feature on the workpiece from adistance away from the index feature.
 56. The method of claim 55,wherein detecting at least one edge of an index feature on the workpiecefrom a distance away from the index feature occurs simultaneously withmoving the sensing element along the first path.
 57. The method of claim55, wherein detecting at least one edge of an index feature on theworkpiece from a distance away from the index feature includes detectinga reflected electromagnetic signal reflected from the index feature. 58.The method of claim 52, wherein detecting at least one edge of an indexfeature includes detecting first and second edges of the index featurealong the first path, the method further comprising computing a midpointlocation based on the first and second edges.
 59. The method of claim58, further comprising detecting third and fourth edges of the indexfeature along a second path of movement of the position sensor, andcomputing an estimated center of the index feature based on the first,second, third, and fourth edges.
 60. The method of claim 52, whereinsupporting a manufacturing assembly proximate a surface of the workpieceincludes supporting a manufacturing assembly having a controlleroperatively coupled to the sensing element, and wherein moving thesensing element along a first path includes transmitting at least onecontrol signal from the controller.
 61. The method of claim 52, whereinsupporting a manufacturing assembly proximate a surface of the workpieceincludes supporting a manufacturing assembly having a drive assemblyoperable to move the sensing element relative to the workpiece, andfurther having a controller mounted on the carriage assembly andoperatively coupled to the drive assembly.
 62. The method of claim 52,wherein supporting a manufacturing assembly proximate a surface of theworkpiece includes supporting a manufacturing assembly having a toolassembly engageable with the workpiece, the method further comprisingoperatively engaging the tool assembly with the workpiece.
 63. A methodof performing a manufacturing operation on a workpiece, the methodcomprising: supporting a manufacturing assembly proximate a surface ofthe workpiece, the manufacturing assembly including a track assemblyattached to the workpiece and a carriage assembly moveably coupled tothe track assembly, the carriage assembly having a drive assemblyoperable to translate the carriage assembly along the track assembly,the manufacturing assembly further including a controller mounted on thecarriage assembly and operatively coupled to the drive assembly; andproviding control signals from the controller to the drive assembly todrive the carriage assembly along the track assembly.
 64. The method ofclaim 63, wherein supporting a manufacturing assembly proximate asurface of the workpiece includes supporting a manufacturing assemblyhaving a sensing element operatively positioned relative to and spacedapart from the workpiece.
 65. The method of claim 64, wherein the driveassembly is further adapted to move the sensor element relative to thecarriage assembly.
 66. The method of claim 64, further comprisingproviding second control signals from the controller to the driveassembly to move the sensor element relative to the carriage assembly.67. The method of claim 64, further comprising detecting at least oneedge of an index feature on the workpiece.
 68. The method of claim 67,wherein detecting at least one edge of an index feature on the workpieceincludes detecting at least one edge of an index feature on theworkpiece from a distance away from the index feature.
 69. The method ofclaim 67, wherein detecting at least one edge of an index feature on theworkpiece including moving the sensing element along a first path. 70.The method of claim 67, wherein detecting at least one edge of an indexfeature on the workpiece includes detecting a reflected electromagneticsignal reflected from the index feature.
 71. The method of claim 67,wherein detecting at least one edge of an index feature includesdetecting first and second edges of the index feature along a firstpath, the method further comprising computing a midpoint location basedon the first and second edges.
 72. The method of claim 71, furthercomprising detecting third and fourth edges of the index feature along asecond path, and computing an estimated center of the index featurebased on the first, second, third, and fourth edges.
 73. The method ofclaim 67, wherein detecting at least one edge of an index featureincludes moving the sensing element along a first path on the workpiece;detecting at least one edge of an index feature on the workpiece;providing a conditioned analog output signal indicating a location ofthe at least one edge of the index feature; and providing a digitaloutput signal indicating the location of the at least one edge of theindex feature.
 74. The method of claim 73, wherein providing an analogoutput signal includes applying a gain and level shift of an analoginput signal to provide the conditioned analog output signal.
 75. Themethod of claim 73, wherein providing a digital signal includesproviding a first digital output signal when the conditioned analogoutput signal is below a threshold level, and providing a second digitaloutput signal when the conditioned analog output signal is above thethreshold level.
 76. The method of claim 63, wherein supporting amanufacturing assembly proximate a surface of the workpiece includessupporting a manufacturing assembly having a tool assembly engageablewith the workpiece, the method further comprising operatively engagingthe tool assembly with the workpiece.